iOS 7 subsidy unlock without restore?

My contract just ended so I requested for my 4S to be unlocked from AT&T, which was just approved.

Normally when you put in the wrong SIM in a locked iPhone it says "Invalid SIM", and in order for the unlock to take place you have to erase and restore the phone.

I popped in a T-Mobile SIM without restoring first just to see what would happen. It said "Searching..." in the upper left for a bit, then it showed the Apple boot screen and restarted. After that it showed "T-Mobile 4G".

Maybe with iOS 7 they let the phone get unlocked without restoring first? If so that's great since the whole erasing and restoring was a major pain in the butt, especially for people who are just switching carriers and not giving/selling the phone.

Anyone else confirm? I don't think this was mentioned anywhere.